import XLSX from 'xlsx'
/*
* 2017-3-27
*author yueshuai
*introduce excel文件导出依赖于  xlsx
*/

var tmpDown; //导出的二进制对象
export default {
	install(Vue) {
		Vue.prototype.downloadExl = function(json,s_n,type) {
			var keyMap = []; //获取键
			for (var k in json[0]) {
				keyMap.push(k);
			}
			var tmpdata = []; //用来保存转换好的json
			json.map((v, i) => keyMap.map((k, j) => Object.assign({}, {
				v: v[k],
				position: (j > 25 ? getCharCol(j) : String.fromCharCode(65 + j)) + (i + 1)
			}))).reduce((prev, next) => prev.concat(next)).forEach((v, i) => tmpdata[v.position] = {
				v: v.v
			});
			var outputPos = Object.keys(tmpdata); //设置区域,比如表格从A1到D10
			var tmpWB = {
				SheetNames: [s_n], //保存的表标题
				Sheets: {
					[s_n] : Object.assign(
						{},
						tmpdata, //内容
						{
							'!ref': outputPos[0] + ':' + outputPos[outputPos.length - 1] //设置填充区域
						}
					)
				}
			};
			tmpDown = new Blob([s2ab(XLSX.write(tmpWB, {
					bookType: (type == undefined ? 'xlsx' : type),
					bookSST: false,
					type: 'binary'
				} //这里的数据是用来定义导出的格式类型
			))], {
				type: ""
			}); //创建二进制对象写入转换好的字节流
			var href = URL.createObjectURL(tmpDown); //创建对象超链接
			document.getElementById("hf").href = href; //绑定a标签
			document.getElementById("hf").click(); //模拟点击实现下载
			setTimeout(function() { //延时释放
				URL.revokeObjectURL(tmpDown); //用URL.revokeObjectURL()来释放这个object URL
			}, 100);
		}
	}
}

function s2ab(s) { //字符串转字符流
	var buf = new ArrayBuffer(s.length);
	var view = new Uint8Array(buf);
	for (var i = 0; i != s.length; ++i) view[i] = s.charCodeAt(i) & 0xFF;
	return buf;
}
// 将指定的自然数转换为26进制表示。映射关系：[0-25] -> [A-Z]。
function getCharCol(n) {
	let temCol = '',
		s = '',
		m = 0
	while (n > 0) {
		m = n % 26 + 1
		s = String.fromCharCode(m + 64) + s
		n = (n - m) / 26
	}
	return s
}